1. Field of the Invention
The present invention relates to a static switch control device synchronized with a passage to zero of the supply voltage (alternating or rectified).
2. Description of the Prior Art
The advantages of firing a static switch at zero voltage are described, in particular, in copending U.S. patent application Ser. No. 367,938, filed on June 7, 1973, now U.S. Pat No. 3,848,158. In the prior art, a known static relay comprises a thyristor-type switch for a rectified current, or a triac or group of thyristors for an alternating current. The control current of this switch is supplied by an auxiliary thyristor placed between a main electrode and the gate control electrode of the static switch, and may be supplied via a rectifier bridge. An active circuit element, such as a transistor, is disposed between the gate and the cathode of the auxiliary thyristor. This transistor short-circuits the closing signal when the feed voltage is greater than a threshold value. However, while the thyristor is desensitized in this way with respect to the closing signal, it can still be fired by parasitic voltage gradients occurring between its anode and its cathode, or by internal leakage currents which occur when the junctions are at a high temperature and the anode - cathode voltage is also high.